Cartridges of highly pressurized gas are used in certain high power staple guns, nail drivers and other similar tools. They are also commonly used to inflate airbags on vehicles, and as a propellant in certain non-lethal weapons. This type of cartridge usually comprises a cylindrical casing with a length of 30 millimeters (1.2 inch), and a diameter of 6 millimeters (0.24 inch). The walls of the cartridge or at least one of its ends is thin enough to be easily punctured in order to release the pressurized gas.
The loading and sealing of such a cartridge is particularly problematic when the contents is pressurized around or above 70 Atmospheres (1,030 psi). One of the most advanced methods taught by the prior art consists in soldering together two sections of the cartridge filled with the pressurized fluid, then evacuating the chamber to retrieve the loaded cartridges. Typically, the presoldered overlapping sections of the separate portions of the cartridges are brought together in the pressurized atmosphere then heated by some induction process to melt the solder, and left to cool down before the high pressure chamber is evacuated.
In the first place, this process can not be practiced when the fluid content is pressurized to a liquid form. Secondly, the soldering may be affected by the expansion and constriction of part of the fluid around the solder-heating process, resulting in leakage or weak soldering points. Moreover, there is no practical way to verify that indeed the cartridge is properly sealed, and that no fluid has escaped during the chamber evacuation process. Similarly, there is no practical way to verify that the pressure is maintained during the life of the cartridge and that the fluid has not slowly leaked out through imperfections in the soldered interface.
While the loading of a defective cartridge in a staple gun may have little consequences, the use of a defective cartridge in an automobile airbag or a weapon may have disastrous consequences.
The present invention results from a quest for a more effective and safe process to package a highly pressurized fluid into a small cartridge.